The invention relates to a viscous coupling having a coupling housing, at least one coupling hub coaxially and rotatably received therein and annular coupling plates which are designed as overlapping outer and inner plates, which are non-rotatingly connected to the housing and coupling hub via corresponding profiles consisting of projections and indentations, and arranged in a certain sequence so as to be alternately distributed in the interior between the coupling housing and coupling hub along the axes thereof, and further having a fluid at least partialling filling the remaining space.
Such viscous couplings are known from GB-PS 1 357 106, for example, where the outer plates, on their outer circumference, comprise teeth by means of which they are accommodated in corresponding teeth of the coupling housing. The inner plates, in their bore, are also provided with teeth by means of which they are received in outer teeth of the coupling hub. Such viscous couplings are used especially in drivelines of motor vehicles either to achieve a distribution of power between the two driven axles or to be able, at least partially, to lock the differential function between the two driven wheels of one axle when one wheel slips in order to generate traction.
Viscous couplings preferably operate with a silicone oil as fluid which is sheared between the coupling plates. Such viscous couplings operate in two different modes, i.e. in the so-called viscous mode and the hump mode. In the case of the viscous mode, the fluid is subject to a pure shear effect in the region between the coupling plates, whereas in the hump mode, the inner and outer plates are subject to friction locking relative to each other and, in the process, transmit a very much higher torque than in the viscous mode. In consequence, the load resulting from the form-fit between the respective coupling part and the associated plates is correspondingly higher.